This invention relates to the field of slider lifters and more particularly relates to slider lifters incorporating shape memory alloys.
Various electromechanical devices have been proposed utilizing shape memory alloys. Among these are: Perry U.S. Pat. No. 3,483,360; Willson U.S. Pat. No. 3,594,674; Willson et al U.S. Pat. Nos. 3,613,732; 3,634,803; and 3,652,969; Du Rocher U.S. Pat. Nos. 3,676,815 and 3,707,694; Hickling U.S. Pat. No. 3,849,756; Clarke U.S. Pat. No. 3,872,415; Jost et al U.S. Pat. No. 3,968,380; Melton et al U.S. Pat. No. 4,205,293; Brubaker U.S. Pat. No. 4,517,543; and Sims U.K. Patent Application 2,026,246A.
These devices typically take advantage of the shape memory effect to trip a switch or break a contact upon reaching a critical temperature.
The phenomenon of shape memory is, of course, well known. The ability to possess shape memory is a result of the fact that the shape memory alloy undergoes a reversible transformation from an austenitic state to a martensitic state with a change in temperature. An article made of such an alloy is easily deformed from its original configuration to a new configuration when cooled below the temperature at which the alloy is transformed from the austenitic state to the martensitic state. The temperature at which this transformation begins is usually referred to as the M.sub.s temperature and the temperature at which this transformation is complete is the M.sub.f temperature. When an article thus deformed is warmed to the temperature at which the alloy starts to revert back to austenite, referred to as the A.sub.s temperature, the deformed object will begin to return to its original configuration. The reversion of the alloy will be complete upon reaching the A.sub.f temperature.
The shape memory alloys that have been used with the above actuators are usually either copper-based or nickel/titanium-based. These alloys are well known to those skilled in the art.
Those who are familiar with computers are aware of so-called Winchesters which are units for storing data on hard discs. The units basically consist of a disc drive unit, a hard disc and a read/write head or slider for retrieving data from the hard disc. The slider is typically cantilevered over the hard disc from a supporting structure by a flexure arm. Other types of disc drive units are configured in a similar manner.
The slider rests on a landing zone on the disc while the power is off. In operation, the drive unit is powered up and the disc begins to rotate. After the disc reaches a certain speed, the slider rises up slightly off the landing zone due to small air currents which push up on the slider. However, until the slider rises, there is considerable friction associated with head drag on the disc which causes wear to the slider and the disc. When the unit is powered down, the same friction occurs until the disc stops rotating.
In order to accommodate this friction, the discs are coated with a protective layer and lubricants are applied. Additionally, the discs often require a landing zone where no data can be stored. Consequently, the amount of data that can be stored on a disc is reduced. Too, a larger disc drive motor is required to overcome the adverse frictional effects and a motor brake is often necessary to stop the rotation of the disc when the motor is turned off to reduce frictional wear.
It can thus be appreciated that it would be desirable to raise the slider during power up and keep it raised during power down so as to eliminate the adverse effects of friction.
Accordingly, in Japanese Patent Application No. 57-222046 and Yaeger et al U.S. Pat. No. 4,551,974, it has been proposed to utilize shape memory alloys to cause the slider to be raised or lowered. In each of these references, the shape memory alloy element works in conjunction with a biasing means which also happens to be the flexure arm.
The difficulty with these references, most apparent with the Japanese reference, is that alteration of the characteristics of the flexure arm is required to make the device work. The lack of commercial success of these devices is due, at least in part, to this fact. Disc drive manufacturers are loathe to change any aspect of the flexure arm. The reason for this attitude is that the combined flexure arm and slider are very sensitive as to their loading and airfoil characteristics. A great deal of time and effort has gone into their design. Accordingly, any design that requires the assistance of the flexure arm, and thus a redesign of the flexure arm as well, is looked upon with disfavor.
Therefore, it is an object of the invention to have a device to raise and lower the slider without adversely affecting the flexure arm.
It is a further object of the invention to have such a device which is simple in design and economical to produce.
These and other objects of the invention will become more apparent after referring to the following description considered in conjunction with the accompanying drawings.